1. Field of the Invention
The present invention relates to an inverter control circuit, and more particularly, to an apparatus for controlling power factor compensation and method thereof, in which a delay of a turn-on timing point of a power factor compensation switch is controlled to enhance a power factor.
2. Discussion of the Related Art
Generally, an air conditioner is a home appliance for maintaining a room air optimal to its usage and purpose. For instance, the air conditioner controls the room air to provide a cooling state to a room in summer or a heating state to the room in winter. The air conditioner adjusts humidity within the room. And, the air conditioner refines the room air into a clean and pleasant state.
As convenient home appliances such as the air conditioner propagate to become popular in use, the user's demand for high energy efficiency, performance enhancement, and convenience of the products rises.
Moreover, as home appliances and electronic devices are popular in home, companies, and factories, many countries regulate the product standards in many aspects. For instance, the harmonic standard regulates to restrict an amount of distorted frequencies. As harmonic hindrance accelerates degradation of various power devices, their endurances are shortened, the danger of fire due to overheating and the like is aggravated, and null power increases to waste power consumption.
In order to solve the above problem, an inverter air conditioner performs various kinds of controls for power factor enhancement to lower the harmonic hindrance.
A power factor enhancement circuit of a general inverter air conditioner is explained as follows.
FIG. 1 is a diagram of a power factor enhancement circuit of a general inverter air conditioner according to a related art.
Referring to FIG. 1, a power factor enhancement circuit of a general inverter air conditioner according to a related art consists of a reactor 102 displaying reactance passing a specific frequency among an input AC power 101, a rectifier 103 having a bridge diode 104 and smoothing capacitors C1 to C3 to convert AC power to DC power, an inverter 105 inverting DC power to AC power to drive a motor 106, an input current detector 107 detecting an input current, a zero crossing detector 108 detecting a zero crossing point of the input AC power 101, a DC link voltage detector 109 detecting a rectified DC voltage, a power factor compensator 110 controlling power factor compensation by a power factor compensation control signal, and a microcomputer 120 controlling the inverter 105 using data detected from the input current detector 107, the zero crossing detector 108, and the DC link detector 109 and controlling a power factor compensation switch to turn on/off.
The power factor compensator 110 consists of a bridge diode 111 connected to an input AC link and a power factor compensation switch 112 connected to the bridge diode 111 to actively vary a harmonic noise and an output voltage by controlling a switch-on/off by the power factor compensation control signal. The power factor compensation switch 112 uses an IGBT (insulated fate bipolar transistor) module for example.
An operation of the above-configured power factor enhancement circuit of the related art inverter control circuit is explained with reference to the drawing as follows.
Referring to FIG. 1, once the power factor enhancement circuit is driven, the AC power 101 is rectified by the bridge diode 104 of the rectifier 103 via the reactor 102, is smoothened by the smoothing capacitors C1 to C3, and is then outputted as the DC power. The DC power rectified in the rectifier 103 is converted to the AC power by the inverter 105 to be supplied as a drive power of the motor 106.
In doing so, the microcomputer 120 outputs a PWM (pulse width modulation) signal to an inverter driver (not shown in the drawing) to drive the inverter 105.
The input current detector 107 detects the input current. The zero crossing detector 108 detects the zero crossing point through a phase of the input current. And, the DC link voltage detector 109 detects the DC voltage of the DC link rectified by the rectifier 103.
In doing so, the microcomputer 120 receives the size of the input current detected by the input current detector 107, the zero crossing point of the input voltage detected by the zero crossing detector 108, and the DC link voltage detected by the DC link voltage detector 109.
The microcomputer 120 detects the phase of the input voltage and the DC voltage and then controls a switching operation of the power factor compensation switch 112 of the power factor compensator 110. For this, the microcomputer 120 commands a turn-on operation of the power factor compensation switch 112 in case that the phase of the input voltage meets the zero crossing point, whereby the power factor compensation switch 112 is turned on by the corresponding signal.
While the power factor compensation switch 112 is turned on, the input voltage is caught on the reactor 102 and the phase of the current passing through the reactor 102 linearly rises to be adjusted close to a phase of a voltage waveform. In doing so, the DC voltage rectified by the rectifier 103 is supplied to the motor 106 via the inverter 105.
FIG. 2 is a diagram of a waveform of an input current for turning on/off a power factor compensation switch, in which (a) indicates a phase of input voltage V and input current I, (b) represents a power phase detection waveform, and (c) indicates an on/off timing diagram of a power factor compensation switch.
Referring to FIG. 2, a power factor compensation switch (SW, IGBT) is turned on at a zero crossing timing point Pz of an input current I or input voltage V. Once a DC link voltage reaches a target voltage after turning on the power factor compensation switch, it is controlled that the power factor compensation switch is turned off to sustain its off-state until a zero crossing point of a next input voltage. The zero crossing timing points Pz according to the detection of the input power are divided by period. And, one switching operation is performed each period. In this case ‘I’ means an ideal input current waveform.
The on-operation of the power factor compensation switch 112 is repeated by taking the zero crossing timing point of the phase of the input voltage as a period. When the target DC link voltage becomes equal to a current DC link voltage after turning on the power factor compensation switch, the power factor compensation switch is turned off. In doing so, if the power factor compensation switch 112 is turned off, a voltage resulting from subtracting the input voltage from the output voltage is applied to the reactor 102 and the reactor current is linearly lowered to the contrary to the on-operation of the power factor compensation switch 112. The on-operation or off-operation of the power factor compensation switch is performed once each zero crossing timing point of the phase of the inputted voltage.
FIG. 3 is a flowchart of a power factor enhancement method in an inverter circuit according to a related art.
Referring to FIG. 3, the zero crossing timing point of the input voltage is detected by the zero crossing detector (S101). The power factor compensation switch (IGBT) is turned on at the detected zero crossing timing point of the input voltage (S103). The DC link voltage detected by the DC link voltage detector is then compared to the target DC voltage to find out whether the DC link voltage coincides with the target DC voltage (S105). If the DC link voltage coincides with the target DC voltage, the power factor compensation switch is turned off (S107). In doing so, the target DC link voltage is set to the DC link voltage providing the highest power factor is set to the target DC voltage.
However, since the switch of the power factor compensator is turned on at the zero crossing timing point of the power voltage, the related art puts limitation on the power factor enhancement. Namely, after the zero crossing time pint has been detected regardless of a load, the power factor compensation switch is turned on and off each uniform interval. Hence, it is unable to uniformly control the power factor for a wide operational range of the load, whereby the power factor enhancement is limited.
And, the related art power factor enhancement circuit is used for the purpose of power factor enhancement only and uses the DC voltage determined by the motor efficiency. Yet, operational efficiency is lowered in case of deviation from a motor design point despite being excellent at the rated voltage.
Moreover, if the DC voltage needed by the circuit is low, it may be difficult to control the DC voltage uniformly.